For a living trust it wouldn't matter (which is why I mentioned the step-up), but what if the trust was a QPRT or other irrevocable trust? Mom could still be living there and the transfer could have happened long ago.
Well, if it was a grantor trust it wouldn't matter, but yes, there are some kinds of trusts where the basis could have been established in the past. However, most likely it was a living trust.
If it was a kind of trust where the transfer happened a long time ago, then there would be no current step up in basis, and no capital gains exclusion, therefore the parties would be paying long term capital gains tax on any gains.
The should probably consult a tax professional with the trust in hand.